1. Field of the Invention
The present invention relates to a photoresist composition, a coating method thereof, a method of forming an organic film pattern using the same, and a display device fabricated thereby, and more particularly, to a photoresist composition for coating onto a large substrate with improved coating uniformity to prevent occurrence of stains, a coating method thereof, a method for forming an organic film pattern using the same, and a display device fabricated thereby.
2. Description of the Related Art
A liquid crystal display (“LCD”) is one of various types of flat panel display that are currently and widely used. An LCD is configured by arranging a thin film transistor substrate with pixel electrodes formed on a surface thereof, and a color filter substrate with a common electrode formed a surface thereof, so that the surfaces of the thin film transistor substrate having the pixel electrodes and the surface of the color filter substrate having the common electrode are held opposite and coplanar to each other at a fixed distance, and interposing a liquid crystal layer between the opposing surfaces of the thin film transistor substrate and the color filter substrate. Images are displayed on such an LCD by applying a voltage to the pixel electrodes and the common electrode to rearrange liquid crystal molecules in the liquid crystal layer so that the amount of light transmitted through the liquid crystal layer is controlled.
Recently, as the demand for large LCDs increase, a commensurate increase in the size of the substrate for such LCDs is inevitably required. Therefore it is necessary to develop a new photoresist composition with coating uniformity suitable to fabricate a large substrate.
“Coating uniformity”, as used herein, means the degree of uniformity of thickness of an organic film that is coated on a substrate. Coating uniformity has an influence on aperture ratio, resolution, circuit line width, and the like, during post-processing. Due to the reflectivity difference that results from minute thickness differences in the organic film, any defects that occur in the organic film are also revealed in the final product.
Furthermore, when fabricating a large LCD, conventional photoresist composition coating methods such as roll coating, spin coating, slit and spin coating, or the like, are not sufficient to coat a photoresist composition onto a large substrate with the required coating uniformity. In particular, it is impossible to coat a conventional photoresist composition onto a large substrate by spin coating, as the durability of a spin motor for a spin coating apparatus that would ordinarily be used would be insufficient given the size of the substrate.
A slit nozzle coating device has therefore been suggested as a coating device for a large substrate. When such a slit nozzle coating device is used, it is possible to reduce the amount of photoresist composition consumed, and further it is not necessary to carry out an edge bead removal process to remove any concentrated photoresist composition from an edge of a substrate, in comparison with the need to remove the edge bead that accumulates with a conventional spin coating process. However, the slit nozzle coating device causes resin streaks, and also produces cumulous stains, neither of which is generated by the conventional spin coating process.
A resin streak is classifiable as either or both of a small streak, which is caused by either or both of a non-uniform penetration of photoresist composition into the substrate, or by discharge of a non-uniform amount of photoresist composition from a slit nozzle occurring at a starting point on a substrate; and a large streak created around the centerline along the coating direction.
The cumulous stain may be created over a portion of the substrate, or the entire area of the substrate, and is mainly caused by non-uniformity of the coating thickness.
The presence of streaks and/or stains increases the defect ratio for the entire process and reduces the quality of the final product. Therefore, a photoresist composition that is suitable for coating large substrates and which satisfies the process requirements of high light transmissivity and sensitivity at the same time is desired. However, conventional polyacrylate based resin materials are limited as to either or both of high transmissivity and sensitivity. Therefore, a novel photoresist composition that can replace the conventional polyacrylate based resins is required.